Systematic review and meta-analysis: the basics explained, quick and easy
New postgraduate students and early career researchers looking for the perfect study design for their research question often ask “what is a systematic review?”. The video below will explain what a systematic review is – a brief and easy-to-understand clarification with an example.
The JBI methodology for systematic reviews is rigorous and scientifically sound. I follow this methodology for all the systematic reviews I conduct. Here is a link to the JBI Manual of Evidence Synthesis. Here is a link to the systematic review referred to in the video above.
Now that you know what a systematic review is, your next quest is to figure out what type of systematic review to conduct. I remember when I did my first systematic review, I tried to force my research question to fit into an effectiveness systematic review. I wanted to determine which factors are associated with injury in cricket fast bowlers, however, at that time, I was new to systematic reviews, and all of it was so overwhelming. I approached my systematic review as if it was a systematic review of effectiveness; you know where two treatments are being compared to see which one wins. While actually, it was a systematic review of etiology, where one relates factors to a certain outcome. Huge difference! It caused a lot of confusion and frustration. But actually, now that I look back, it seems a bit silly that I struggled so much to get my head around it.
Yes, in both cases, the overarching principles are the same. You collect your primary studies and summarise them into one systematic review, but the detail in terms of how you present and analyse your results is different. Also, at that time, there was very little guidance on how to do a systematic review, while now, we are blessed with a whole lot of smart people out there who help and guide us. A research group led by Zachary Munn wrote the paper “What kind of systematic review should I conduct? A proposed typology and guidance for systematic reviewers in the medical and health sciences” published in BMC Medical Research Methodology. This is a super valuable article when it comes to figuring out what type of systematic review you need to do according to what you want to achieve.
All the different reviews are listed and explained in Table 1 of the article. In this video, I’ll briefly go through the different types, and then I’ll leave you to go and read the article.
The different types of systematic reviews are:
• Effectiveness reviews
• Experiential (Qualitative) reviews
• Costs/Economic Evaluation reviews
• Prevalence and/or Incidence reviews
• Diagnostic Test Accuracy reviews
• Etiology and/or Risk reviews
• Expert opinion/policy reviews
• Psychometric reviews
• Prognostic reviews
• Methodological systematic reviews
In the article of Munn et al. you’ll find references to more information on each of these types of systematic reviews. They even refer to an example of each of these types of systematic reviews. You can also find more information in the JBI Manual for Evidence Synthesis.
Now that you know the various types of systematic reviews out there, what’s the next step? Watch the video below for a bit more of a detailed explanation, then download the paper of Munn et al and save it in a safe place, bookmark the JBI Manual for Evidence Synthesis, decide which type of systematic review suits your research question best, and download a few examples of this type of systematic review. A good place to get examples from is the journal JBI Evidence Synthesis; you will be able to download their protocols for free, which is already of great help. And then Google Scholar may be able to assist with examples of full systematic reviews. Also, read the relevant chapter in the JBI Manual for Evidence Synthesis. And then, get going!
Now that you know what a systematic review is and that there are many different types of systematic review, you may ask, what is the difference between a systematic review and a meta-analysis? Or, is a systematic review the same as a meta-analysis? Let me explain.
The researchers who conduct the systematic review may do a meta-analysis as part of the systematic review. A meta-analysis is done by taking the results from each primary study, pooling these results together and re-analyse them to look at the effectiveness of balance exercises across all studies. A meta-analysis can’t always be done. To do a meta-analysis, the primary studies that are being pooled together, need to be similar enough to one another. Or in some cases, the primary studies consist of qualitative data, where for example, interviews with participants were done, in which case no statistical analysis can be done.
How do you know whether a published study is a systematic review or a systematic review with a meta-analysis? You’ll often see that the title of the publication states whether it’s a systematic review or a systematic review and meta-analysis, although this is not always the case and then you may pick up from the abstract whether a meta-analysis was also done. If it's still not clear, you can go to the methods and results section to see if the results from all these studies were analysed statistically.
To summarise, a systematic review refers to the summarising of primary studies into one study, using rigorous and systematic methods, while a meta-analysis refers to the statistical analysis used to pool all the findings from the different primary studies into one analysis. Not all systematic reviews include a meta-analysis, but all meta-analyses are part of a systematic review. The video below will add more clarity to this concept.
Now that you know what a systematic review is, that there are different types of systematic reviews out there and that the concept of a meta-analysis is no longer a foreign one, you are ready to dive in. When you are ready to plan your systematic review search strategy, this blog post will help a lot. Another tip is to explore Covidence systematic review software. The team over at Covidence is doing a great job in making the lives of systematic reviewers easy by providing us with a user-friendly platform to help streamline the import, screening and extraction process and automatically populate the PRISMA flow diagram for you. The Systematic Reviews playlist on the Research Masterminds YouTube channel is another valuable source of valuable how-to's.
And... the best is... when you join the Research Masterminds Success Academy, you can get access to Covidence at a reduced price. The Research Masterminds Success Academy is an awesome membership site for postgraduate students - a safe haven offering you coaching, community and content to boost your research experience and productivity. Check it out! https://researchmasterminds.com/academy.
Photo by Canva Studio